Let’s just start with the premise that the next pool you dive into will contain pee. Because it probably will. There’s also probably going to be a wee bit of fecal matter, a dollop of human sweat and some guy’s skin cells floating around.

Swimming pools are basically huge blue toilet bowls. We’ve all peed in them — be honest — and a new study is stirring up our guilt by showing that urinating in a chlorinated pool creates a toxic chemical called cyanogen chloride. Cyanogen chloride forms when ...